The common technology for extracting gases such as hydrogen from industrial streams, for use in the electronics industry for hydrogenation or for changing the balance of hydrogen in those streams is to use membranes. The membranes are disposed in a housing. A mixed gas flow is conducted to the housing wherein the extraction occurs. Extracted gas (such as hydrogen) is preferentially extracted through the membranes and exits through an outlet port. A second outlet allows for the exhaust of raffinate out of the chamber, Examples of such chambers are shown in U.S. Pat. Nos. 5,205,841, and 4,468,235.
Many protocols require the mixed gas to be at elevated temperatures. In such cases, heat is lost from the housing, through the housing walls or carried away with the extracted gas, thereby resulting in loss of thermal efficiency of this system. Furthermore, heating methods currently in use tend to produce large thermal gradients, with the gas extraction membrane often being heated excessively in some areas and being under heated in others. The result of this is decreased flow rates and/or damage to the membranes. Johnson Matthey, LTD, has used a system of multiple heaters and temperature controllers, but this approach is energy inefficient and does not control the temperature much better than the single heater as the multiple controllers often fight one another. A system that helps to conserve heat and avoid these problems is disclosed in the pending U.S. application Ser. No. 08/875,046, published as WO 97/17125 to the inventor of the present invention.
Raffinate flow control and safety are also problems with the currently available purification and generation systems. The inventor has observed an input gas explosion during hot start up. Similarly, explosive conditions can result from a cool down in air where the module, full of combustible gas, sucks air in through the raffinate port. In either case, an explosive mixture of air and gas mixture suddenly contacts a hot membrane and thus creates a serious danger. This danger is all the more severe as if the present invention is used as a hydrogen generator to fuel a fuel cell, e.g., to run a car, because of the demanding operating environment and the variety of mechanical talent, and the desire for a unit can be turned on or off instantly.
Pure gas suck-back can also ruin a membrane if the sucked-back gas has already been mixed with a component, like arsine, that can poison the membrane. Purified hydrogen is mixed with arsine in the manufacture of semiconductors.